As the level of integration in semiconductor devices has increased, advances have been achieved in reducing the size of their component elements. Thin films of ferroelectrics with extremely high specific dielectric constants have gained attention for application to dynamic memory DRAMs, which require especially small capacitors with a high capacitance. Publicized examples include that of P. J. Bhattacharya et al. Jpn. J. Appl. Phys. Vol. 32 1993, pp. 4103-4106.
According to the disclosure of Bhattacharya et al., when a film of Ba, SrTiO.sub.3 referred to hereinafter as BST was formed on a Pt substrate, it was discovered that the crystals of the film grew in columnar fashion, making it possible to obtain a high specific dielectric constant of approximately 300. However, when these thin films were used to form capacitors, although it was possible to form capacitors with very good insulating characteristics, many of them had a high leakage current. This was not satisfactory for obtaining a yield sufficient for the mass production of VLSIs such as DRAMs. Based on a detailed study of the reasons for this, it can be surmised that a leakage current was passing through the crystal grain boundaries of the ferroelectric thin film. The objective of the present invention is to provide semiconductor devices and their fabrication method which comprise ferroelectric thin films for capacitors that make it possible to obtain a yield sufficient for applications to VLSIs.
In addition, semiconductor devices, especially DRAMs, require capacitors with small surface areas. Ferroelectric thin films consisting of Ba, SrTiO.sub.3, Pb Zr, TiO.sub.3, etc. which have extremely low specific dielectric constants have gained attention for use in obtaining such capacitors. When these thin films are used to form capacitors, it is possible to form capacitors with extremely good insulating characteristics. However, many of them have a high leakage current. Thus, it is not possible to obtain a yield sufficient for applications to ULSIs such as DRAMs. The objective of the present invention is to provide a charge-storage capacitor ferroelectric thin film and fabrication method with which it is possible to obtain a yield sufficient for mass production in applications to ULSIs.